1. Field of the Invention
The present invention relates to 4-nitrosodiphenylamine derivatives that are useful as coupling agents for carbon black filled rubber compounds.
2. Description of Related Art
Fillers, such as carbon black, are added to elastomeric compounds for a variety of reasons. They act as low cost diluents and as reinforcing agents, giving higher modulus, higher strength and wear resistance. The interaction between a filler and an elastomer matrix is also very important to the development of desirable dynamic properties. It is known that dynamic properties are improved when a carbon black filler is bonded to an elastomer matrix. This is evidenced by lower hysteresis, which results in lower rolling resistance when the rubber is used to make automobile tires. An additional benefit of better elastomer-filler interaction is improved traction when the rubber is used in tire treads. Improved bonding between the polymer and filler can also result in a cured rubber exhibiting lower heat build-up.
In the absence of interaction between the filler and the elastomeric matrix, the filler forms a loosely bonded network within the matrix, which remains after curing. When the dynamic storage modulus, designated G′, is measured in the cured rubber sample, the filler network acts to increase the modulus. As the applied strain on the rubber sample is increased, the bonds that form this filler network are broken and it no longer contributes to the modulus. Thus, in the absence of coupling between the filler and the elastomer matrix, the dynamic storage modulus, G′, will diminish as an applied strain is increased. This is known as the Payne Effect.
When the filler and the elastomer matrix are coupled, no filler network forms in the cured elastomer. Thus, when an applied strain is increased as the dynamic measurement is made, the storage modulus, G′, does not decrease as rapidly with an increase in the strain. This diminution of the Payne Effect is also taken as evidence that coupling has taken place.
In the past, some chemicals have been added to rubber to improve the interaction of carbon black with the rubber matrix. For example, N-methyl-N,4-dinitrosoaniline was used, but it was discontinued due to concerns about its toxicity. Benzofurazan oxides have also been reported to be effective coupling agents, but upon curing they evolve an undesirable odor.
The use of 4-nitrosodiphenylamine as a promoter for the interaction of carbon black and rubber has also been suggested. The chemical is an effective promoter, but its usefulness is limited by a pronounced tendency to affect the processability of the rubber by dramatically reducing the scorch safety of the rubber compound.
U.S. Pat. No. 4,557,306 discloses carbon black products, said to be useful in rubber compositions, and rubber compositions (uncured or cured) containing said carbon black products comprising carbon black having a surface area of at least 20 m2/g. and up to about 10% by weight, based on the weight of the carbon black of at least one aromatic furazan oxide. Useful furazan oxides have both carbons of the furazan ring as part of a fused aromatic ring, and particular examples include benzofurazan oxide, and its methyl and methoxy analogs. It is disclosed that filled rubber vulcanizates containing the carbon black products exhibit many improved properties, such as increased filler-rubber interaction and decreased hysteresis, and that tires made from them show lower running temperatures and improved rolling resistance.
U.S. Pat. No. 4,570,690 discloses filled rubber vulcanizates containing aromatic furazan oxides that are said to exhibit many improved properties, such as increased filler-rubber interaction and decreased hysteresis. Useful furazan oxides have both carbons of the furazan ring as part of a fused aromatic ring. Typical examples are benzofurazan oxide and its methyl and methoxy analogs. It is further disclosed that tires made from the vulcanizates show lower running temperatures and improved rolling resistance and that the desirable effects of the aromatic furazan oxides may be improved by mixing the rubber, filler and furazan oxide in a conventional mechanical compounding device at specific temperatures and time periods, such as about 200°-400° F. for 2-20 minutes.
U.S. Pat. No. 4,751,271 discloses modified polymer rubber compositions prepared in solution that are said to exhibit desirable properties, particularly when used to form tires. The modified rubber compositions comprise the reaction product, prepared in solution, of at least one rubber having an unsaturated carbon chain and up to about 10 weight percent, based on the weight of the rubber, of at least one aromatic furazan oxide of the partial formula wherein the depicted carbon atoms are a part of a single fused aromatic ring. The reaction is conducted by heating the solution at an elevated temperature which may be any temperature up to the decomposition temperature of the furazan oxide. The uncured polymer rubber compositions do not have the strong characteristic odor of the furazan oxide decomposition products which facilitate handling and storage of these materials. Filled vulcanizates also are described, and these vulcanizates are prepared by vulcanizing a composition comprising at least one of the above-described uncured polymer rubber compositions and one or more reinforcing fillers normally used in rubber compounding. It is further disclosed that the filled vulcanizates exhibit desirable properties such as decreased hysteresis, increased rebound and, when used in the tread of tires, the tires show lower running temperatures and reduced rolling resistance.
U.S. Pat. No. 4,788,229 discloses that uncured modified rubber compositions can be prepared by a process which comprises the steps of (A) preparing a first mixture comprising an elastomer, at least one reinforcing filler and at least one chemical agent capable of promoting the formation of filler-elastomer linkages; (B) preparing a second mixture comprising (i) an elastomer, at least one reinforcing filler and at least one chemical agent capable of promoting the formation of filler-elastomer linkages, wherein at least one of the elastomer, filler or chemical agent in the second mixture is different from the elastomer, filler or chemical agent in the first mixture; or (ii) an elastomer and at least one reinforcing filler; or (iii) at least one reinforcing filler and at least one chemical agent capable of promoting the formation of filler-elastomer linkages; or (iv) an elastomer and at least one chemical agent capable of promoting the formation of filler-elastomer linkages; and (C) blending the first and second mixtures to form a third mixture. Examples of such chemical agents include aromatic furazan oxides, heterocyclic di-N-oxides, 1-hydroxy-benzimidazole-3-oxide compounds, 1,3-dihydroxy-benzimidazolinone compounds, and aromatic nitroso compounds.
Morita, E., Rubber Chem. Technol, 49(4):1019-30 (1976) elucidated the mechanism of reactions of N,4-dinitroso-N-methylaniline (DNMA) with polymers and its promotion of carbon black reinforcement in polymers by spectrophotometric observations of the factors that influence these reactions and the functionality of the two dissimilar nitroso groups of DNMA.
Stefanowski, T., Polimery, 12(12):571-3 (1967) coated carbon black with couplers, then extracted with benzene to remove uncombined material, then compounded into rubber. N,4-dinitroso-N-methylaniline, dihydroxynitrosobenzoquinone (Vulkafor BQN), pentachlorothiophenol, hexachlorocyclopentadiene, 2,6-dichloro-4-nitrophenol, and tetrachloroquinone were tested. Pentachlorothiophenol and hexachlorocyclopentadiene increased interaction of the carbon black with rubber. See CA 69: 20179t.
Devrits, Y. et al., Kauch. Rezina, 26(3):14-17 (1967), disclosed that carbon black in rubber with N,4-dinitroso-N-methylaniline gives improved properties, including heat build up. CA 67: 22668j
Walker, L. A. et al., Rubber Age, 90(6):925-931 (1962), disclosed that the use of N,4-dinitroso-N-methylaniline in natural rubber, SBR-, and NR-SBR-carbon black stocks brings about increased modulus, reduced hysteresis, and lower heat build-up. The reaction was carried out in a Banbury mixer by simultaneous mixing of the chemical with rubber and carbon black at a temperature of 150° C.
Leeper, H. M. et al., Rubber World, December 1956 pp. 413-428, disclosed that the properties of butyl rubber vulcanizates can be improved by chemical modification of the polymer with N-methyl-N,4-dinitrosoaniline.
Graves, D. F., Rubber Chem. and Technol, 66(l):61-72 (1993), showed that benzofuran 1-oxide, commonly called benzofuroxan (BFO), decreased hysteresis of carbon black-filled rubber vulcanizates by as much as 30%. BFO was added during the mixing of the masterbatch at various temperatures. It was found that high temperature mixing was necessary to achieve maximum hysteresis reduction and that more effect was noted with high surface are blacks. Nickel salts were found to modify the reaction between BFO and the elastomer/black.
Ceausescu, E. et al., J. Macromol. Sci.-Chem, A22(5-7):1013-32 (1985), explained the mechanism of the action of nitroso derivatives on the basis of the theory that the reinforcing effect is due to the strain-crystallization process. CA 103: 23606m
Zyuzin, A. P., Kauch. Rezina, 1983 (10):11-13, showed that the addition of p-nitrosodiphenylamine enhanced the absorption of SKI-3 rubber on the surface of carbon black and reduced hysteresis losses. The modification of PM-100 black-filled isoprene tread rubbers with oligodienes decreased the content of bound rubber and increased hysteresis losses, presumably due to competing adsorption of rubber and oligodiene macromolecules on the surface of the carbon black. CA 99: 213920f
Shvarts, V. et al., Kauch. Rezina, 1982(6):24-6, disclosed that SKI or SKD rubber modified with p-nitrosodiphenylamine gives better properties including resilience, tear, tensile, modulus. A three-pass mix with separate introduction of carbon black is required. CA 97: 56916y.